SONET

INTRODUCTIONDigital transmission standards for fiber-optic cable

Independently developed in USA & EuropeSONET (Synchronous Optical Network) by ANSISDH (Synchronous Digital Hierarchy) by ITU-T

Synchronous network using synchronous TDM multiplexing

All clocks in the system are locked to a master clock

It contains the standards for fiber-optic equipments

SONET was originally designed for the public telephone network.

A bit-way implementation providing end-to-end transport of bit streams.

Multiplexing done by byte interleaving.

SONET commonly transmits data at speeds between 155 megabits per second (Mbps) and 2.5 gigabits per second (Gbps).

One of SONETs most interesting characteristics is its support for a ring topology .

Very flexible to carry other transmission systems (DS-0, DS-1, etc)

SONET LAYERS SONET defines four layers: path, line, section, and photonic

Path layer is responsible for the movement of a signal from its optical source to its optical destination

Line layers is for the movement of a signal across a physical line

Section layer is for the movement of a signal across a physical section, handling framing, scrambling, and error control

Photonic layer corresponds to the physical layer of OSI model

Architecture of a SONET system: signals, devices, and connections

Signals: SONET(SDH) defines a hierarchy of electrical signaling levels called STSs (Synchronous Transport Signals, (STMs)). Corresponding optical signals are called OCs (Optical Carriers)

Devices: STS Multiplexer/ Demultiplexer, Regenerator, Add/Drop Multiplexer and Terminals

Connections: SONET devices are connected using sections, lines, and paths

Section: optical link connecting two neighbor devices: mux to mux, mux to regenerator, or regenerator to regenerator

Lines: portion of network between two multiplexers

Paths: end-to-end portion of the network between two STS multiplexers

SONET FRAMES Each synchronous transfer signal STS-n is composed of 8000 frames. Each frame is a two-dimensional matrix of bytes with 9 rows by 90 n columns.

A SONET STS-n signal is transmitted at 8000 frames per second

Each byte in a SONET frame can carry a digitized voice channel In SONET, the data rate of an STS-n signal is n times the data rate of an STS-1 signal

In SONET, the duration of any frame is 125 s

SONET NETWORKS

1. Point-to-point network :2. Multipoint network :

Ring Network: UPSR Unidirectional Path Switching Ring (UPSR)

Ring Network: BLSR Bidirectional Line Switching Ring (BLSR)

Mesh NetworkRing network has the lack of scalabilityMesh network has better performance

SONET AdvantagesReduced network complexity and cost

Allows transportation of all forms of traffic

Efficient management of bandwidth at physical layer

Standard optical interface

De-multiplexing is easy.

SONET DisadvantagesStrict synchronization schemes required

Complex and costly equipment as compared to cheaper Ethernet

SYNCHRONOUS DIGITAL HIERARCHY (SDh)

INTRODUCTIONStandard for interfacing optical networks

Simple multiplexing process

SDH is basically the international version of SONNET

SONNET is NORTH AMERICAN version of SDH

SDH frame structure STM-1 frame is the basic transmission format for SDH Frame lasts for 125 microseconds It consists of overhead plus a virtual container capacity

SDH network elementsRegenerator (Reg.)

Terminal Multiplexer (TM)

Add/Drop Multiplexer (ADM)

Digital Cross Connect (DXC)

REGENERATORIt mainly performs 3R function:1R Reamplification2R Retiming3R ReshapingIt regenerates the clock and amplifies the incoming distorted and attenuated signal. It derive the clock signal from the incoming data stream.

Terminal Multiplexer (TM)

It combines the Plesionchronous and synchronous input signals into higher bit rate STM-N Signal.

Add/Drop Multiplexer (ADM)STM-NSTM-NPDHSDHAdd / Drop Multiplexer

Digital Cross Connect (DXC)

TYPICAL LAYOUT OF SDH LAYER

General view of Path Section designations

SDHmultiplexerSDH Regenerator

#Cross- connectSDHmultiplexerSDHSDHSDHPDHATMIPRegenerator SectionRegenerator SectionMultiplex SectionMultiplex SectionPath

Network Configurations

Point to Point Point to Multipoint Mesh Architecture Ring Architecture

SDH Advantages

Allows multi-network internetworking

SDH is synchronous

Allows single stage multiplexing and de-multiplexing

DENSE WAVELENGTH DIVISION MULTIPLEXING

THE GENERAL STRUCTURE OF THE DWDM SYSTEM

Multiple channels of information carried over the same fibre, each using an individual wavelengthDense WDM is WDM utilising closely spaced channelsChannel spacing reduced to 1.6 nm and less Cost effective way of increasing capacity without replacing fibreAllows new optical network topologies, for example high speed metropolitian rings

Wavelength Division MultiplexerWavelength Division Demultiplexerl1Al2l3BCl1Xl2l3YZl1 + l2 + l3Fibre

ITU Recommendation is G.692 "Optical interfaces for multichannel systems with optical amplifiers"G.692 includes a number of DWDM channel plansChannel separation set at:50, 100 and 200 GHz equivalent to approximate wavelength spacings of 0.4, 0.8 and 1.6 nmChannels lie in the range 1530.3 nm to 1567.1 nm (so-called C-Band)Newer "L-Band" exists from about 1570 nm to 1620 nmSupervisory channel also specified at 1510 nm to handle alarms and monitoring

Optical Spectral Bands

TransmittersDWDM MultiplexerPower AmpLine AmpLine AmpOptical fibreReceive PreampDWDM DeMultiplexerReceiversEach wavelength behaves as if it has it own "virtual fibre"Optical amplifiers needed to overcome losses in mux/demux and long fibre spans

THE ERBIUM DOPED FIBER AMPLIFIERS (EDFA)MULTIPLEXERSDEMULTIPLEXERS ADD/DROP MULTIPLEXEROPTICAL SWITCH.

DWDM AdvantagesGreater fibre capacityEasier network expansionNo new fibre neededJust add a new wavelengthIncremental cost for a new channel is lowNo need to replace many components such as optical amplifiersDWDM systems capable of longer span lengthsTDM approach using STM-64 is more costly and more susceptible to chromatic and polarization mode dispersionCan move to STM-64 when economics improve

DWDM DisadvantagesNot cost-effective for low channel numbersFixed cost of mux/demux, transponder, other system componentsIntroduces another element, the frequency domain, to network design and managementSONET/SDH network management systems not well equipped to handle DWDM topologiesDWDM performance monitoring and protection methodologies developing

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